Olefin-based polymers such as ethylene-based polymers and/or propylene-based polymers are produced via various catalyst systems. Selection of such catalyst systems used in the polymerization process of the olefin based polymers is an important factor contributing to the characteristics and properties of such olefin-based polymers.
Ethylene-based polymers, such as, polyethylene is known for use in the manufacture of a wide a variety of articles. The polyethylene polymerization process can be varied in a number of ways to produce a wide variety of resultant polyethylene resins, having different physical properties that render the various resins suitable for use in different applications. It is generally known that ethylene-based polymers can be produced in solution phase loop reactors, in which ethylene monomer, and optionally one or more alpha olefin comonomers, typically having from 3 to 10 carbon atoms, are circulated in the presence of one or more catalyst systems, under pressure, around a loop reactor, by a circulation pump. The ethylene monomers, and optionally one or more comonomers, are present in a liquid diluent, such as an alkane or isoalkane. Hydrogen may also be added to the reactor. The catalyst systems for producing ethylene-based polymers may typically comprise a chromium-based catalyst system, a Ziegler Natta catalyst system, and/or a molecular (either metallocene or non-metallocene) catalyst system. The reactants in the diluents, and the catalyst system, are circulated, at an elevated polymerization temperature, around the loop reactor, thereby producing polyethylene homopolymer and/or copolymer, depending on whether or not one or more comonomers are present. Either periodically, or continuously, part of the reaction mixture, including the polyethylene product dissolved in the diluent, together with unreacted ethylene and one or more optional comonomers, is removed from the loop reactor. The reaction mixture, when removed from the loop reactor, may be processed to remove the ethylene-based polymer product from the diluent and the unreacted reactants, with the diluent and unreacted reactants typically being recycled back into the loop reactor. Alternatively, the reaction mixture may be sent to a second reactor, e.g., a loop reactor, serially connected to the first loop reactor, where a second polyethylene fraction may be produced.
Despite the research efforts in developing catalyst systems suitable for polyolefin, such as polyethylene and/or polypropylene, polymerization, there is still a need for a pro-catalyst and a catalyst system, exhibiting high reactivity toward hydrogen, and capacity for producing higher molecular weight polymers; thus, facilitating the production of highly linear polymers under optimum polymerization conditions. Additionally, despite the research efforts in developing polyolefins, such as polyethylene and/or polypropylene, with improved properties, there is still a need for a polyethylene having improved properties. These needs have been met by the following invention.